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Summary
Some of the headwater streams and rivers of the Rangitikei River that originate in the Ruahine Ranges have populations of the threatened blue duck/whio (Hymenolaimus malacorhynchos). This duck species is restricted mainly to fast-flowing and turbulent rivers and streams in forested hill country and mountains. Numbers have declined significantly since European settlement due to land use change and introduced predators.
While predators are likely the main determinant of breeding success of whio, their food supply is also vitally important. There is concern to what the impacts of the invasive algae, Didymosphenia geminata (Didymo) would be on duck populations. There is the potential that this algae, if introduced to the blue duck rivers of the Ruahine Ranges, would alter the benthic macroinvertebrate community and thus impact on the blue duck diet.
This survey provides a snapshot of the macroinvertebrate and algal communities of four sites on headwater streams of the Rangitikei River catchment within the Ruahine Forest Park. These sites were in streams known to have populations of whio. Should Didymosphenia geminata ever become established, this data will provide an indication of previous conditions.